Compact power transfer unit

ABSTRACT

A motor vehicle power transfer unit includes an input portion, an output portion, a non-parallel gear set and a parallel gear set. The input portion is adapted to connect to an output portion of a transmission assembly and the output portion is adapted to connect to an input portion of a rear wheel drive line. The parallel gear set is coupled to the input portion and transfers power to the non-parallel gear set, which is coupled to the output portion. The non-parallel gear set includes a ring gear having a front face with gear teeth formed therein and a rear face having a cavity formed therein. The ring gear is supported within the power transfer unit by a bearing mounted within the cavity.

BACKGROUND

[0001] 1. Field of the Invention

[0002] The present invention relates to the power train of a motorvehicle. More specifically, the present invention relates to a powertransfer unit in the power train for distributing power to the front andrear wheels of the vehicle.

[0003] 2. Description of the Prior Art

[0004] In the past, most automobiles in the United States utilized arear wheel drive power delivery scheme. In adapting these rear wheeldrive schemes into four wheel drive applications, a transfer case was,and often still is, positioned at the output of the transmissionassembly. When engaged, the transfer case diverts a portion of the powercoming from the transmission assembly from the rear wheels to the frontwheels.

[0005] Currently in the United States, a significant portion (if not amajority) of new automobiles are front wheel drive based vehicles. In afront wheel drive vehicle, both the engine and the transmission assemblyare typically transversely oriented in the vehicle. By positioning thepower plant and transmission assembly transversely in the vehicle, moredirect coupling of the transmission assembly to the vehicle's transaxleand front wheels can be achieved. In doing so, a front wheeldifferential is incorporated directly into the transmission assemblyitself.

[0006] With front wheel drive vehicles themselves becoming a maturemarket, a recent trend in the automobile industry has been to adaptthese front wheel drive schemes for all or four wheel driveapplications. This is accomplished by providing a power transfer unitthat diverts a portion of the power from the front wheels to a rearwheel drive shaft and subsequently the rear wheels.

[0007] While prior power transfer units work sufficiently well for theirintended purposes, their construction limits the extent to which theirsize can be reduced (thereby making the engine bay unavailable for othercomponents). This also limits packaging flexibility of the unitsthemselves. Normally front differentials in transaxles are of the beveltype and require a large amount of axial space along a directiontransverse to the vehicle. As the transaxle package grows axially, itinterferes with having equal length halfshafts and furthermore steering,suspension, and engine mount/roll restrictor placement.

[0008] As a way of maximizing manufacturing resources, it is alsodesirable to develop automotive products that can be utilized andincorporated across a variety of platforms. When incorporated into avehicle, the power transfer unit is attached to the output face of thevehicle transmission. It is therefore in close proximity to the engine,the transmission, the steering rack and the exhaust manifold.Additionally, new PZEV catalytic converters are required to be locatedcloser to the exhaust manifold so that they can achieve a quicker“light-off” of the catalyst. These PZEV catalytic converters also tendto be larger and generate higher temperatures than previous non-PZEVcatalytic converters. The proximity to the engine, transmission and theother under hood components accordingly limits the size of the powertransfer unit. Further, the high temperature of “manicat” catalyticconverters and the previously mentioned PZEV catalytic converters meansthat polymer based products, such as lubricants and seals, need to beplaced at as great a distance as possible from the PZEV catalyticconverter.

[0009] One manner in which the overall size of the power transfer unitcan be reduced is to similarly reduce the size of the gears, bearingsand shafts of the power transfer unit itself. However, reducing the sizeof these components limits their overall torque carrying capacity.

[0010] An end result of all of the above is a desire for lateralcompactness in the design of the power transfer unit. By compacting thislateral size of the power transfer unit, the power transfer unit can beconfigured as multiplatform assembly, in that the system itself can bedesigned for the worst case scenario, in other words the minimum lateralwidth available for a power transfer unit.

[0011] In order to achieve the greatest lateral compactness possible,the gears and bearings located inside the power transfer unit need to belocated in the most space efficient manner possible. This can result inconflicts in the sizing and shaping of various components of the unit.

[0012] It is therefore an object of the present invention to overcomethe above and other limitations of the prior art and to provide a morecompact power transfer unit, thereby increasing the available packagingspace in the motor vehicle's engine bay.

SUMMARY OF THE INVENTION

[0013] The present invention overcomes the limitations of the prior artby providing a power transfer unit with more compact packaging of thecomponents therein, thereby allowing the power transfer unit to be morecompact in size.

[0014] The power transfer unit includes an input portion that is adaptedto connect to an output portion of a transmission assembly, and anoutput portion that is adapted to connect to an input portion of therear wheel drive line. A parallel gear set and a non-parallel gear setare coupled between the input portion and the output portion of thepower transfer unit.

[0015] In a first aspect of the present invention, the non-parallel gearset includes a ring gear having a front face with gear teeth formedtherein and a rear face having a bearing seat formed therein. The ringgear is supported within the power transfer unit by a bearing mountedwithin the bearing seat of the rear face.

[0016] In another aspect of the present invention, the non-parallel gearset is a bevel gear set having a ring gear coupled to the parallel gearset and a pinion gear coupled to the output portion of the powertransfer unit.

[0017] In still another aspect of the present invention, the parallelgear set includes an input gear coupled to the input portion and anoutput gear coupled to the non-parallel gear set.

[0018] Additional objects and features of the present invention will bereadily apparent to those skilled in the art from a review of theattached drawings, the following detailed description and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a partial break-away view of a first embodiment of apower transfer unit as described in the claims;

[0020]FIG. 2 is a partial break-away view of a second embodiment of thepower transfer unit;

[0021]FIG. 3 is a layout view of the input portion, parallel gear set,non-parallel gear set, and output portion of the power transfer unit asdescribed in the claims; and

[0022]FIG. 4 is a side sectional view of an output gear of the parallelgear set and a ring gear of the non-parallel gear set of the powertransfer unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Referring now to the drawings, FIG. 1 illustrates a powertransfer unit 10 having a housing 12 within which the primary componentsof the power transfer unit 10 are packaged. The power transfer unit 10includes an input portion 14 adapted to connect to a transmission (notshown) of an automobile, and an output portion 16 adapted to connect toa rear drive line (not shown) of the automobile. A parallel gear set 18is coupled to the input portion 14, and a non-parallel gear set 20 iscoupled to the output portion 16.

[0024] As used herein, the term “parallel gear set” is intended to referto any mechanism (including, without limitation, mechanisms with gears,gear wheels, mechanisms without gear wheels, gear trains, chain gearsand belt systems), which transfers power from a first shaft to a secondshaft; the first and second shafts defining axes that are generallyparallel to one another.

[0025] As used herein, the term “non-parallel gear set” is intended torefer to any mechanism (including, without limitation, mechanisms withgears, gear wheels, mechanisms without gear wheels, gear trains, chaingears and belt systems) for transferring power from a first shaft to asecond shaft; wherein the first and second shaft define axes that arenot generally parallel to one another.

[0026] As mentioned above, the primary components of the power transferunit 10 are all integrally packaged together and provided within acommon housing 12. The input portion 14 and the output portion 16 may ormay not protrude from the housing 12 depending on the specific designcriteria of the power transfer unit 10 and the application in which itis being employed.

[0027] Rotation from a transmission assembly is coupled to the inputportion 14 of the power transfer unit 10. The input portion 14 iscoupled to the parallel gear set 18 such that rotation from thetransmission is transferred to the parallel gear set 18.

[0028] The parallel gear set 18 includes, at least, an input gear 22 andan output gear 24. The input portion 14 of the power transfer unit 10extends outward from the input gear 22 and includes either an internalor external spline adapted to engage an output from the transmission ofthe vehicle. The input portion 14 could include other features such as aflange, or threaded engagement to allow the input portion 14 of thepower transfer unit 10 to engage the transmission.

[0029] In a first embodiment, the parallel gear set 18 is a three axisparallel gear set, as shown in FIG. 1. The three axis parallel gear setadditionally includes an idler gear 26. Rotation is transmitted to theinput gear 22 from the input portion 14, from the input gear 22 to theidler gear 26, and from the idler gear 26 to the output gear 24. Asshown, the input gear 22, the idler gear 26, and the output gear 24 allrotate about axes which are parallel to one another, and transverse tothe vehicle.

[0030] Alternatively, the parallel gear set 18 can be a two axisparallel gear set, as shown in FIG. 2, wherein the input gear 22 and theoutput gear 24 directly engage one another such that rotation istransmitted directly from the input gear 22 to the output gear 24. Theinput gear 22 and the output gear 24 all rotate about axes which areparallel to one another, and transverse to the vehicle. In either of theembodiments shown in FIGS. 1 and 2, the input gear 22, the output gear24, and the idler gear 26, if one is being incorporated, can be eitherhelical gears or spur gears.

[0031] As an alternative a chain or belt (not shown) could be used tointerconnect the input gear 22 and the output gear 24. Additionally, therelative diameters of the gears 22, 24, 26 may be the same or different,as determined by design criteria not relevant to an understanding of thepresent invention.

[0032] The non-parallel gear set 20 includes a bevel ring gear 28 and abevel pinion gear 30. The ring gear 28 is coupled to the output gear 24such that rotation from the parallel gear set 18 is transferred to thering gear 28 of the non-parallel gear set 20. The pinion gear 30 iscoupled to the output portion 16 of the power transfer unit 10 such thatrotation is transferred from the ring gear 28 to the pinion gear 30 andthrough the pinion gear 30 to the output portion 16 of the powertransfer unit 10.

[0033] Referring to FIG. 3, a layout view of the three axis powertransfer unit 10 is shown wherein the rotational movement is transferredinto the power transfer unit 10 through the input portion 14; from theinput portion 14 through the input gear 22, the idler gear 26, and theoutput gear 24; from the output gear 24 of the parallel gear set 18 tothe ring gear 28 of the non-parallel gear set 20; across thenon-parallel gear set 20 from the ring gear 28 to the pinion gear 30;and from the pinion gear 30 to the output portion 16 of the powertransfer unit 10.

[0034] The ring gear 28 is mounted within the housing 12 in a mannerthat enables the ring gear 28 to rotate about a first axis 32 whichextends transversely relative to the vehicle. The ring gear 28 includesa front face 32 and a rear face 34. The front face 32 of the ring gear28 includes gear teeth 35 adapted to engage corresponding gear teeth 37on the pinion gear 30. The pinion gear 30 is mounted within the housing12 in a manner that enables the pinion gear 30 to rotate about a secondaxis 38 which is oriented generally perpendicular to the first axis 32and extends longitudinally with respect to the vehicle in theillustrated embodiment.

[0035] While not readily apparent in the Figures, the first and secondaxes 32, 38, about which the ring gear 28 and the pinion gear 30respectively rotate, may be oriented such that the axes 32, 38 intersectone another or do not intersect one another. In the latter situation,the non-parallel gear set is seen to be a hypoid bevel gear set.

[0036] Referring to FIG. 4, the rear face 36 of the ring gear 28includes a cavity 40 formed therein. The cavity 40 defines a bearingseat 41. The ring gear 28 is mounted within the housing 12 and supportedtherein by a bearing 42 that fits within the bearing seat 41. An outerrace of the bearing 42 is received by and supported within the bearingseat 41. An inner race of the bearing is, in turn, supported directly onthe radial surface of a boss 43 formed in the housing 12. By embeddingthe bearing 42 within the rear face 36 of the ring gear 28, the width ofthe power transfer unit 10 can be decreased without requiring a smallerbearing, and providing enhanced lateral compactness. Further, bymounting the bearing 42 directly within the ring gear 28, the ring gear28 is directly positioned with respect to the housing 12, the amount ofstack-up error within the components is reduced, and concentricitybetween the ring gear 28 and the bearing 42 is maintained.

[0037] Finally, by incorporating the support bearing 42 within a cavity40 formed in the rear face 36 of the ring gear 28, the width of thepower transfer unit 10 can be compacted, thereby allowing the powertransfer unit 10 to be designed for smaller packaging situation withoutsacrificing the power or durability of the power transfer unit 10.

[0038] The output gear 24 is supported on a transfer shaft 44. Thetransfer shaft 44 has a first end 44 a that is supported by a bearing46, and a second end 44 b that is supported directly on the bevel ringgear 28. The output gear 24 can be integrally formed with the transfershaft 44, or the output gear 24 can be mounted onto the transfer shaft.The transfer shaft 44 engages the bevel ring gear 28 by being press fit,splined, or by other suitable means, such that the transfer shaft 44 issupported solely by the bearing 46 and the bevel ring gear 28.

[0039] By utilizing the parallel gear set 18 and the non-parallel gearset 20, it becomes possible to locate the parallel gear set 18 tightlyagainst the housing (not shown) of the transmission assembly. This ispossible because the non-parallel gear set 20 requires less longitudinalspace than would a comparable parallel gear set. With the parallel gearset 18 located adjacent to the transmission assembly, reduced “roll”forces are experienced by the transmission assembly and the remainder ofthe drive chain.

[0040] Use of the parallel gear set 18 and the non-parallel gear set 20also more readily allows the drive line to be moved to the centerline ofthe vehicle and at the desired height. If the non-parallel gear set 20were employed to move the drive line back to the vehicle's centerline,large diameter gears or gear rings would need to be used, creatingadditional problems relating to packaging size and other constraints.

[0041] The foregoing discussion discloses and describes a preferredembodiment of the invention. One skilled in the art will readilyrecognize from such discussion, and from the accompanying drawings andclaims, that changes and modifications can be made to the inventionwithout departing from the true spirit and fair scope of the inventionas defined in the following claims.

I claim:
 1. A motor vehicle power transfer unit for distributing torquebetween a front wheel drive line and a rear wheel drive line, said powertransfer unit comprising: a housing; an input portion adapted to connectto an output portion of a transmission assembly; an output portionadapted to connect to an input portion of the rear wheel drive line; aparallel gear set and a non-parallel gear set coupled between said inputportion and said output portion of said power transfer unit; and saidnon-parallel gear set including a ring gear having a front face withgear teeth formed therein and a rear face having a bearing seat formedtherein, said ring gear being supported within said power transfer unitby a bearing mounted within said bearing seat, said bearing beingsupported by a boss formed in said housing.
 2. The power transfer unitof claim 1 wherein said non-parallel gear set is a bevel gear set. 3.The power transfer unit of claim 2 wherein said bevel gear set is ahypoid bevel gear set.
 4. The power transfer unit of claim 1 whereinsaid parallel gear set includes an input gear and an output gear, saidinput gear being an input into said parallel gear set.
 5. The powertransfer unit of claim 4, further including a transfer shaft having afirst end a and a second end, said first end being supported by abearing mounted within said power transfer unit and said second endbeing supported directly on said ring gear.
 6. The power transfer unitof claim 5 wherein said output gear is integrally formed with saidtransfer shaft.
 7. The power transfer unit of claim 5 wherein saidoutput gear is mounted onto said transfer shaft.
 8. The power transferunit of claim 5 wherein said transfer shaft is mounted in said frontface of said ring gear.
 9. The power transfer unit of claim 4 whereinsaid parallel gear set is a two-axis gear set such that said input gearengages said output gear.
 10. The power transfer unit of claim 4 whereinsaid parallel gear set is a three-axis gear set including and idler gearsuch that said input gear engages said idler gear and said idler gearengages said output gear.
 11. The power transfer unit of claim 4 whereinsaid non-parallel gear set is a bevel gear set having a ring gearcoupled to said output gear and a pinion gear.
 12. A motor vehicle powertransfer unit comprising: a housing; an input portion adapted to connectto an output portion of a transmission assembly; an output portionadapted to connect to an input portion of the rear wheel drive line; anon-parallel gear set mounted between and interconnecting said inputportion and said output portion, said non-parallel gear set including aring gear having a front face with gear teeth formed therein, and a rearface having a bearing seat formed therein, said ring gear beingsupported within said power transfer unit by a bearing mounted withinsaid bearing seat, said bearing being supported by a boss formed in saidhousing.
 13. The power transfer unit of claim 12 wherein saidnon-parallel gear set is a bevel gear set.
 14. The power transfer unitof claim 13 wherein said ring gear of said bevel gear set is coupled tosaid input,portion.
 15. The power transfer unit of claim 14 wherein saidnon-parallel gear set further includes a pinion gear coupled to saidoutput portion of said power transfer unit.
 16. The power transfer unitof claim 15 wherein said bevel gear set is a hypoid bevel gear set. 17.The power transfer unit of claim 12 further including a parallel gearset mounted between input portion and said output portion, said parallelgear set coupled to said non-parallel gear set.
 18. The power transferunit of claim 17 wherein said parallel gear set includes an input gearand an output gear, said input gear being an input into said parallelgear set.
 19. The power transfer unit of claim 18 further including atransfer shaft having a first end a and a second end, said first endbeing supported by a bearing mounted within said power transfer unit andsaid second end being supported directly on said ring gear.
 20. Thepower transfer unit of claim 19 wherein said output gear is integrallyformed with said transfer shaft.
 21. The power transfer unit of claim 19wherein said output gear is mounted onto said transfer shaft.
 22. Thepower transfer unit of claim 19 wherein said transfer shaft is mountedin said front face of said ring gear.
 23. The power transfer unit ofclaim 18 wherein said parallel gear set is a two-axis gear set whereinsaid input gear engages said output gear.
 24. The power transfer unit ofclaim 18 wherein said parallel gear set is a three-axis gear setincluding and idler gear wherein said input gear engages said idler gearand said idler gear engages said output gear.